1. Field of the Invention
The invention relates to telephone switching offices which utilize electromechanical or electronic switching equipment. In particular, the invention relates to a method and apparatus for providing the switching equipment with the capability of controlling the connection, management and disconnection of telephone circuits using Signaling System #7, (SS7 ), a national and international standard set of protocols for providing such circuits control, and providing and receiving information via the SS7 protocol for enabling enhanced services in the switching equipment.
2. Description of the Prior Art
The existing telephone network in the United States of America is largely a remnant of the earlier AT & T Network which was divested into several regional holding companies pursuant to an order of a Federal Court. This existing network had been designed to provide the equivalent of an electrical connection between two points in the network. The only information originating within the telephone network, and the conveyance of this information, was related to the provision of a basic capability to connect the two points.
Advances in the state of the art of communications have lead to the possibility of providing the existing services of the telephone network in a more efficient manner while simultaneously establishing the foundation for new network services beyond the capability of the existing network. The realization of this possibility has resulted in both national and international development of new standards for communication protocols between the switching elements within the telephone network. These new standards are widely referred to as "Signaling System #7 (SS7 )". For example, see TR-NPL-000246 "Bell Communications Research Specification of Signaling System No. 7, Revision #2, 6/87."
Until now, the provision of SS7 capability within electromechanical switching systems has not been accomplished and thus, with the current art, would require the replacement of the switch with a newer version. The difficulty of accomplishing the conversion of such electromechanical and electronic switches is demonstrated by the inability of the trunk circuit interfaces on these switches to support the out-of-band signaling method employed by SS7 and by the lack of the capability for processing the SS7 protocol messages used to implement the services.
As the majority of telephones in the United States of America are connected to crossbar offices, 1ESS (a Trademark of AT&T Technologies, Inc.) or 1AESS (a Trademark of AT&T Technologies, Inc.) switches, the replacement or upgrading of these switches would require vast economic expenditures by the telephone companies. Estimates of this replacement cost for a typical central office are frequently in excess of $3 million. The incurring of such costs for the replacement of switching equipment which is functioning well is not justified by initial increases in revenues from the provision of more efficient switching.
The present invention provides a method and apparatus for implementing SS7 capabilities within Class 5 central offices such as the 1/1A ESS (a Trademark of AT&T Technologies, Inc.) and the No. 5 Crossbar. This is accomplished without affecting the underlying operating principles of the existing switching office. In addition, the SS7 capability is provided in a cost effective manner without adversely affecting the quality of service as perceived by the subscribers connected to such a switching office. Further, the SS7 capability is provided in such a manner so as not to adversely affect the operation of the upgraded switching office or the rest of the telephone system.
The SS7 protocol requires that the control signals for the management of the telephone circuits be transmitted from the calling switching office to the receiving switching office on a separate circuit from the trunk circuit on which the telephone message information is transmitted.
The present invention provides a subscriber line interface which is interposed between the calling subscriber and the existing telephone switching system for generating a signal representing the calling number, monitoring the status of the subscriber lines and, when necessary, examining the dialed digits from the calling subscriber. The present invention also includes a receiver module interposed between the existing switching matrix and the existing digit receiver for examining the dialed digits to identify the specific call and the type of trunk circuit required (i.e. SS7, non-SS7 or intra-office). A trunk circuit interface is also coupled to the existing switching system for generating a trunk circuit identification signal which is related to the specific call. A processing unit is coupled to the subscriber line interface, the receiver module, and the trunk circuit interface for receiving the signals representing the calling number, the called number, and the trunk circuit identification, all of which are related to the specific call. These signals are then transmitted on a separate line to the receiving switching office for management of the switching circuits on the receiving end to couple the incoming call to the correct receiving subscriber on the correct trunk circuit.